Windshield for head-up display system

ABSTRACT

A windshield for a head-up display system has a pair of opposing major surfaces that are nonparallel to one another in selected areas. Light rays directed toward the nonparallel area of the windshield are reflected from the outer and inner major surfaces of the windshield and directed toward the eye of the observer as parallel or superimposed light rays to eliminate ghost images when viewing images projected by the head-up display system through the windshield. The interlayer blank utilized to make the windshield has a non-uniform thickness profile with a tapered thickness positioned in the selected areas of the windshield.

RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 08/664,033filed Jun. 13, 1996, now U.S. Pat. No. 5,812,332, which is a divisionalof U.S. patent application Ser. No. 08/038,749 filed Mar. 26, 1993, nowabandoned, which is a continuation-in-part of U.S. application Ser. No.07/747,765 filed Aug. 20, 1991, now abandoned, which is acontinuation-in-part of U.S. application Ser. No. 07/654,408 filed Feb.8, 1991, now abandoned, which is a continuation of U.S. application Ser.No. 07/414,492 filed Sep. 28, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a windshield for a head-up display system andin particular to an automotive windshield functioning as the combinerfor the head-up display system and having a wedged configuration forsome selected portion of the windshield area, particularly in theviewing area of the head-up display, to eliminate double imaging and theinterlayer used to provide the required wedged configuration.

2A. Technical Considerations

A head-up display system is a visual display arrangement that displaysinformation to a viewer while he simultaneously views the road andobjects outside his vehicle around and through the display. Head-updisplay systems are often incorporated into aircraft cockpits for pilotsto monitor flight information. More recently the systems have been usedin land vehicles such as cars, trucks and the like. The display isgenerally positioned so that the viewer does not have to glance downwardto the vehicle dashboard and away from the viewing area in front of thevehicle as is required of a vehicle operator viewing vehicle operatinginformation in a vehicle not having a head-up display.

A head-up display system generally includes a display projection system,a collimator, and a combiner. The projection system includes a lightsource that projects operating information through the collimator whichgenerally aligns the projected light rays. The collimated light is thenreflected off the combiner, which is in the vehicle operator's field ofview. In this manner, vehicle information such as, for example, fuelinformation and vehicle speed is displayed within the operator's fieldof vision through the windshield and permits the operator to safelymaintain eye contact with the road and other objects outside his vehiclewhile simultaneously viewing the displayed information. The reflectedimages of the display may be focused at a position anywhere fromimmediately in front of the vehicle to optical infinity.

Laminated windshields have been used as the combiner in a head-updisplay system to reflect a primary display image as taught in U.S. Pat.No. 2,264,044 to Lee. However, it has been observed that a secondaryimage is reflected off the outer surface of the windshield. Thissecondary image is superimposed over but offset from the primary imageand reduces the overall image clarity.

It would be advantageous to have a windshield for a head-up displaysystem which functions as a combiner and provides a clear display imagewithout producing double images when viewing through the head-up displayarea, without distorting the view through other portions of the windownot associated with the head-up display system, and withoutincorporating additional components with the windshield.

2B. Patents of Interest

U.S. Pat. No. 1,871,877 to Buckman teaches a display system having aglass sheet mounted on the windshield or dashboard which reflectsinstrumentation information to the vehicle operator.

U.S. Pat. No. 2,264,044 to Lee teaches a motor vehicle having anilluminated speedometer display that is reflected off the inboardsurface of the vehicle windshield.

U.S. Pat. No. 2,641,152 to Mihalakis teaches a vehicle projection devicewherein instrumentation information is reflected off of a reflectingscreen on the inboard surface of the vehicle windshield. The reflectingsurface has a satin finish and can be metal, glass, or plastic.

U.S. Pat. No. 2,750,833 to Gross teaches an optical display system foreliminating double images which occur in reflector type sights such asthose used in aircraft gun sighting installations. A collimated lightbeam is polarized and separated into two ray branches. One of the tworay branches is then eliminated.

U.S. Pat. No. 3,276,813 to Shaw, Jr. teaches a motor vehicle displaysystem which utilizes a highly reflective coating on the inboard surfaceof the vehicle windshield to reflect instrumentation information to thevehicle operator.

U.S. Pat. No. 3,446,916 to Abel teaches an image combiner utilizing aportion of the aircraft window. The inner surface portion of the windowis coated with a partially reflective film.

U.S. Pat. Nos. 3,554,722, 3,591,261, and 3,647,285 to Harvey et al.teaches a double glazed glass window structure which eliminatesobjectionable fringe patterns produced in this structure when floatglass of non-uniform thickness is utilized. The window structureincludes a pair of spaced apart, float glass sheets one or both of whichare tapered from a thick edge to an opposing thin edge. When both theglass sheets are tapered, the glass sheets are positioned such that athick edge of one glass sheet is spaced from a thin edge of the opposingglass sheet.

U.S. Pat. No. 3,697,154 to Johnson teaches an optical viewing system inwhich images formed on the screen of a cathode ray tube (CRT) arereflected from a curved mirror having a general aspheric surface ofrevolution to a partially reflective combiner having two nonparallelhyperboloid surfaces, the combiner being positioned in the normal lineof sight of an observer such that a collimated CRT image is reflectedfrom the near surface of the combiner to the observer's eyes and thecombiner being adapted to transmit light incident from the outside sothat the CRT display is superimposed without parallax on the real worldto provide a head-up display.

U.S. Pat. No. 3,870,405 to Hedges teaches a visor for use an opticalelement in a helmet-mounted sight having inner and outer surfaces beingsections of focal paraboloids of revolution.

U.S. Pat. No. 3,899,241 to Malobicky, Jr. et al. teaches a windshieldadapted for use in aircraft and includes a transparent reflectivecoating on the inboard surface in the center portion of the forwardvision area to form a vision image receiving area. Vehicle informationis reflected off the reflective coating to the vehicle operator.

U.S. Pat. No. 3,940,204 to Withrington and U.S. Pat. No. 4,218,111 toWithrington et al. teach an optical display system utilizing holographiclenses.

U.S. Pat. No. 4,261,635 to Freeman teaches a head-up display systemincluding a holographic combiner positioned inboard of the vehiclewindshield. The hologram is disposed substantially orthogonal to andmidway along an axis between the observer's eye position and theprojection optics so as to deviate light from an image produced by theprojection optics to the observer eye with minimal field aberration.

U.S. Pat. No. 4,398,799 to Swift teaches a head-up display system whichsimultaneously records the pilot's view by reflecting the outside sceneand the projected display by reflecting the outside scene andsuperimposed display off a mirror mounted on the pilot's helmet andrecording the reflected view with a camera mounted on the pilot'shelmet.

U.S. Pat. No. 4,613,200 to Hartman teaches a head-up display systemwhich uses two parallel holographic optical elements to reflectinstrumentation information to the vehicle operator. One of the elementsis made part of or attached to the vehicle windshield.

U.S. Pat. No. 4,711,544 to Iino et al. teaches a display system for avehicle wherein instrumentation information is reflected off the frontglass of the vehicle so that the image display can be formed in adesired position, aligned with the line of sight of the driver withoutobstructing the front sight of the driver.

U.S. Pat. Nos. 4,787,711 and 4,892,386 and European Patent No. 229,876to Suzuki et al. teach an on-vehicle head-up display device employing acatoptric system for a windshield glass of an automobile to project adisplay image onto an inner surface of the windshield glass, an opticalsystem for letting a virtual image of the display image of the displaymeans enter the windshield glass is adapted to make an angle formed bylight beams of the virtual image entering the windshield glass less thana monocular resolving power and an optical means for correcting parallaxof the light beams of the virtual image is provided between the opticalsystem and the windshield glass to thus eliminate double imaging andbinocular parallax.

Defensive Publication No. T861,037 to Christensen teaches a tapered orwedged vinyl interlayer for use in laminating windshields such that theinterlayer is thicker at the top of the windshield than at the bottom ofthe windshield in order to eliminate double vision caused by thewindshield curvature and angle of installation.

SUMMARY OF THE INVENTION

The present invention provides a windshield for a head-up display systemthat reduces the degree of double imaging that occurs when a laminatedwindshield is used as the combiner in the display system. The windshieldfunctions as a combiner for the head-up display system without requiringany additional reflecting or transmitting elements or components to beincorporated onto or into the windshield assembly. The windshield in thepresent invention is constructed such that selected opposing, outermajor surfaces of the windshield are non-parallel with the opposingouter major surfaces oriented relative to each other so that an image,projected from a display source and reflected off a first major surfaceof the windshield, is substantially superimposed over or parallel to thesame image from the display source reflected off the opposing outermajor surface of the windshield.

In one embodiment of the invention the windshield has a selected areathat has the outer major surfaces of the windshield non-parallel to oneanother, and the outer major surfaces of the windshield at the remainingarea generally parallel to one another. In this manner, the degree ofdouble imaging is reduced in the area where the outer surfaces arenon-parallel to one another, and the optical distortion in the remainingarea is improved because the outer surfaces are parallel to one another.This may be accomplished by having one or both of the glass plies and/orthe sheet of interlayer material partially tapered in thickness suchthat when the plies and sheet are joined together, the outer majorsurfaces of the windshield in the selected area are nonparallel to oneanother with the remaining area of the outer major surfaces of thewindshield generally parallel to one another in the area other.

The present invention also provides an interlayer blank for use with aglass ply in a vehicle windshield for a head-up display system. Theblank is polyvinylbutyral and includes a first portion with apredetermined thickness profile and a second portion with a taperedthickness profile different from the predetermined profile. Theinterlayer may be provided by casting the interlayer to the desiredconfiguration, extruding the desired cross sectional thickness, ordifferentially stretching the interlayer to the desired shape or througha combination of these processes. In one particular embodiment of theinvention, interlayer having a desired varying thickness profile isproduced by initially forming the interlayer with a thickness profilegreater than the desired profile and subsequently differentiallystretching the interlayer to reduce the thickness of the interlayer suchthat its thickness corresponds to the desired thickness profile.

When the glass plies and the interlayer having the tapered section areassembled and laminated to form a unitary structure, the opposing majorsurfaces of the laminate are non-parallel in the area of the taperedsection and offset at a predetermined angle in the vicinity of thetapered section. The windshield in use is positioned relative to adisplay system such that the images generated by light rays from thedisplay source reflected off the non-parallel opposing major surfaces ofthe windshield or laminate are substantially superimposed over orparallel to each other such that double imaging is reduced if noteliminated, while the remaining sections of the windshield have theouter major surfaces substantially parallel to one another to eliminateor minimize optical distortion of objects viewed through the remainingarea of the windshield.

The invention also contemplates making the windshields of the instantinvention by joining glass sheets and a sheet of interlayer material toprovide a windshield having the outer surfaces parallel in a firstpredetermined area and nonparallel in a second predetermined area.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a head-up display system for a vehicle.

FIG. 2 is an enlarged, partial cross-sectional view of FIG. 1illustrating a head up display using a windshield incorporating aninterlayer having a uniform thickness.

FIG. 3 is an enlarged, partial cross-sectional view of FIG. 1illustrating a head up display using a windshield incorporating aninterlayer having a uniformly tapered thickness.

FIG. 4 is an enlarged cross-sectional view of an alternate windshieldconfiguration.

FIGS. 5 and 6 are cross-sectional views of windshield configurationincorporating features of the present invention.

FIG. 7 is a plan view of an interlayer blank of the present invention.

FIGS. 8 through 11 are cross-sectional views of interlayer sheetsincorporating alternate embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the elimination of double imaging in ahead-up display system that uses an automotive windshield as thecombiner, but it should be appreciated that the present invention may beused in any type of combiner having a laminate construction where doubleimaging is to be eliminated.

With reference to FIG. 1, head-up display 10 system includes a motorvehicle windshield 12, an image source 14 and a projection assembly 16,preferably mounted immediately beneath the upper surface of the vehicledashboard 18 and positioned between the image source 14 and windshield12. Light rays emanate from the image source 14 and are projected ontothe windshield 12, which operates as a combiner as will be discussedlater, and reflected into the field of vision of the vehicle operator orobserver 20. The light rays projected onto the windshield 12 arecollimated so as to create a virtual image in front of the car,preferably at about 5 to 50 feet (3 to 15 meters) in front of thewindshield 12.

Although not limiting in the present invention, the image source 14preferably is a transmissive liquid crystal display (LCD) that isadequately illuminated to project information carrying light raysthrough the projection assembly 16 onto the windshield 12 at a locationwithin the vehicle operators direct line of sight while permittingperipheral viewing of the road and objects outside of the vehicle as theoperator or observer 20 monitors the display. It is contemplated thatalternative viewing locations will also provide an effective head-updisplay for the vehicle windshield. The displayed image (not shown) mayinclude numerical or graphical symbols including for example, vehiclespeed, fuel level, engine RPMs, temperature, and warning symbols.

The following discussion will be directed towards the use of a prior.art windshield which incorporates an interlayer having a constantthickness, as the combiner in a head-up display system which projects animage a finite distance in front of the windshield. In particular,referring to FIG. 2, windshield 30 represents a windshield assembly withthe opposing inner and outer major surfaces of the windshield beingparallel to each other for the full length of the windshield, i.e. fromthe top edge to the opposite edge and between the side edges. Thewindshield 30 includes outer glass ply 32 bonded to inner glass ply 34by an interlayer material 36. Because the thickness of the interlayer 36is fairly uniform and the opposing major surfaces of each glass ply aresubstantially parallel to each other, i.e., inner surface 37 of the ply32 is parallel to its outer surface 38 and inner surface 39 of the ply34 is parallel to its outer surface 40, the outer major surface 38 ofthe glass ply 32 is parallel to the outer major surface 40 of the glassply 34 after the glass plies 32 and 34 and interlayer 36 are laminatedtogether to form a unitary structure. Although not limiting in thepresent invention, for the purposes of illustration, surfaces 38 and 40are assumed to be planar in the following discussion. However, thesurfaces may be non-planar, as will be discussed later.

With continued reference to FIG. 2, a light ray A from image source 14is directed along line 42 and a portion of the light ray A is reflectedoff surface 40 of the ply 34 along line 44 to eye 46 of the vehicleoperator 20. Additional light rays from the source 14 are directed alongadditional lines. For example, light ray B is directed along line 48 anda portion of the light ray B is reflected off the surface 40 along line50 toward the vehicle operator 20. However, the ray B along the line 50is not directed to the eye 46 as shown in FIG. 2 so it will not bedetected by the observer 20.

A portion of the light ray B which is directed along line 48 will enterthe windshield assembly 30 and be refracted along line 52. The angulardifference between the lines 48 and 52 depends on the angle ofrefraction as the light ray passes through the air and into the glassply 34. The angle of refraction in turn depends, in part, on the angleat which ray B is incident on the surface 40 and the relative densitiesof the air and the glass. The ray B passes through the windshieldassembly 30 and a portion of the light ray B is reflected off thesurface 38 of the ply 32 along line 54. It is assumed that therefractive index of interlayer 36 is essentially the same as that of theglass plies 32 and 34 so that the light rays are not redirected as theypass through the windshield assembly 30 along lines 52 and 54.

A portion of the light ray B leaves the windshield assembly 30 at thesurface 40 of the glass ply 34 where the direction of the light is againchanged due to the difference in the refraction index between thewindshield assembly 30 and the air, as discussed earlier, and directedalong line 56 to the operator's eye 46. Because the light rays A and Breceived by the eye 46 from the image source 14 are along two differentlines, i.e. lines 44 and 56, which are convergent toward one another tothe eye of the observer 20 rather than parallel, the observer 20 willperceive two offset images where in fact there is only one image source14. The first image 58, or virtual image, is the image seen by theobserver 20 from the portion of the light ray A directed along line 44.The second image 60 is the image seen by the observer 20 from theportion of the light ray B directed along line 56.

When viewing both images, the virtual image 58 will appear brighter thanthe second image 60 because a greater portion of the light from theimage source 14 which was initially directed along line 42 will bedirected along line 44 as compared to the amount of light initiallydirected along line 48 and which is finally directed along line 56 tothe observer 20. This condition of seeing two offset images is commonlyreferred to as double imaging, or ghost imaging, and results when theouter surfaces of the windshield assembly i.e. surfaces 38 and 40 ofwindshield assembly 30, are parallel to each other. Stated another way,double imaging occurs when the light rays A and B, projected from imagesource 14 onto parallel surfaces 38 and 40, are directed toward the eyeof the observer along non-parallel lines, i.e., lines 44 and 56 whichconverge toward each other to the eye 46 of the operator 20.

In order to reduce the amount of double imaging in the windshieldassembly 30, the present invention may be used to modify the windshieldstructure by adjusting the spaced relationship of the surfaces 38 and 40relative to one another such that the portion of the light rays A and Bdirected to the eye of the observer are superimposed over or parallel toone another. Referring to FIG. 3, windshield 130 includes outer glassply 132 bonded to inner glass ply 134 by an interlayer material, e.g., athermoplastic material 136 along inner major surfaces 137 and 139 ofplies 132 and 134, respectively. The interlayer 136 is fabricated insuch a way as to gradually taper in thickness from top to bottom of thewindshield with the thicker section at the top edge as reviewed in FIG.3.

As a result of the “wedged” shape section of the interlayer, when thewindshield components are assembled and laminated, outer major surface138 of glass ply 132 and outer major surface 140 of glass ply 134 willbe non-parallel. It has been found that by controlling the amount bywhich the glass plies 132 and 134 of the windshield 130 are offset fromeach other, the double imaging encountered when using a windshield asshown in FIG. 2 as a combiner can be reduced in a manner to be discussedbelow. The actual wedge angle X required to reduce the double imagingdepends, in part, upon the thickness of the windshield, the windshieldmaterials, and the relative positions and orientations of the imagesource 14, the windshield 130 and the vehicle operator 20. Although notlimiting in the present invention, the interlayer 136 can be cast inplace to provide the desired wedge angle X. As an alternative, theinterlayer 136 can be extruded or differentially stretched in anyconvenient manner known in the art, such as that disclosed in U.S. Pat.No. 4,201,351 to Tolliver and U.S. Pat. No. 4,554,713 to Chabel, whichteachings are incorporated herein by reference, or cast or extruded andsubsequently differentially stretched as will be discussed later in moredetail, to achieve the desired wedge angle.

With continued reference to FIG. 3, the discussion will now be directedto the elimination or minimization of double images or ghost imagesusing a windshield that has wedge or taper, i.e., nonparallel outersurfaces. Light ray A¹ from the image source 14 is directed along line142 and a portion of the light ray A¹ is reflected off the surface 140along line 144 to the eye 46. Another portion of the light ray B¹directed along line 148 is reflected from the surface 140 along line 150such that it is not seen by the observer 20 as was discussed for theportion of the light ray B reflected from the surface 40 along line 50of the prior art arrangement shown in FIG. 2. The remaining portions ofthe ray B¹ are refracted through the glass plies 132 and 134 and theinterlayer 136 along line 152 and refracted as it leaves the assembly130 to the observer's eye 46 along line 144 in a similar manner as thatdiscussed for the ray B shown in FIG. 2. However, unlike the windshieldassembly 30 in FIG. 2 wherein the line 56 from the ray B is along adifferent orientation than line 44 from ray A, in the present inventionas shown in FIG. 3, the wedge angle X is such that the refracted lightfrom light ray B¹ exits the assembly 130 along the line 144, i.e.,parallel or superimposed over the light from ray A¹ reflected off thesurface 140 of the glass ply 134 also moving along the line 144. As aresult, the image viewed by the observer 20 resulting from light rays A¹and B¹ are superimposed over or parallel to each other so that there isviewed only a single image 158.

It should be appreciated that in a windshield assembly, the surfaces 138and 140 of the glass plies 132 and 134, respectively, are often notplanar but rather have a curved configuration. However, the amount ofrelative curvature in the windshield assembly 130 within the small areaused as the combiner is relatively small so that the area within thecombiner portion of the windshield 130 is nearly planar. Furthermore, ifrequired due to excessive curvature of the windshield within thecombiner area, the image from the image source 18 can be distorted, forexample by incorporating additional lens arrangements (not shown) intothe projection assembly 16 (shown only in FIG. 1) to account for thecurvature of the windshield surfaces.

In one particular embodiment of a windshield construction as illustratedin FIG. 3, the windshield 130 includes 0.090 inch (2.3 mm) thick glassplies and two polyvinylbutryl interlayer plies. Each interlayer ply isoriginally 0.020 inches (0.05 mm) thick and is differentially stretchedso that each interlayer ply has a taper of approximately, 0.003 inches(0.076 mm) over a 36 inch (91 cm) interlayer width for a combinedthickness differential of approximately 0.006 inches (0.152 mm) from thetop to the bottom edge (as viewed in FIG. 3) when incorporated into thewindshield 130. It should be obvious to one skilled in the art that thetwo interlayer plies may be replaced by a single ply having the requiredwedge configuration. Referring to FIG. 1, it has been observed that awindshield of this construction, mounted in a vehicle at an installationangle Y of approximately 30° from the horizontal with an angle ofincidence Z between the windshield 12 and image source 14 ofapproximately 65° significantly reduces the amount of double imaging ina head-up display system as compared to a conventional windshield havinga non-wedged configuration.

Although the windshield configuration 130 as shown in FIG. 3 includestwo glass sheets each having generally parallel opposing major surfacesand a tapered interlayer ply, based on the teachings of this disclosure,it is obvious to one skilled in the art that other windshieldconfigurations can be used to provide a wedged windshield configurationsimilar to that shown in FIG. 3. In particular, referring to FIG. 4, oneor both of the glass plies 232 and 234 may be provided with a taper suchthat when the assembly 230 is laminated to form a unitary structureusing a non-stretched interlayer 236, opposing surfaces 234 and 236 ofthe windshield 230 are non-parallel and are oriented relative to eachother so as to eliminate the double imaging. It is further contemplatedthat one or more tapered interlayers may be used in combination with oneor more tapered glass plies so that the final laminated assemblyprovides a required windshield construction having the configurationrequired to reduce double imaging. In other words, the windshieldconfiguration as taught herein to reduce double imaging in a head-updisplay system is not directed to providing glass plies and a sheet ofinterlayer that does or doesn't have a taper as long as after the pliesare secured about the interlayer the outer surfaces of the windshieldare nonparallel so that the portions of the light rays A¹ and B¹directed toward the eye of the observer are parallel or superimposedover one another along the line 144 as shown in FIG. 3.

It is an object of this invention to provide a windshield configurationwherein the outer surfaces of the windshield are non-parallel only inthe head-up display area of the windshield. In this manner, the problemof double imaging of the display is reduced or eliminated while at thesame time optical distortions associated with viewing objects throughwedged glass or a wedged windshield is eliminated. More particularly, ithas been noted that the use of non-tapered or non-wedged areas oflaminated glass, i.e., outer surfaces of the laminated windshield beingsubstantially parallel to one another for the upper portion of awindshield as mounted, with the tapered or wedged areas, i.e. a partialwedge, at or near the bottom of the windshield as mounted, improves theoptics of the windshield. More particularly, a vehicle operator viewingan object such as a traffic light at a 45° angle through an upper areaof the windshield encounters less double vision of objects viewedthrough a non-tapered or non-wedged windshield than a tapered or wedgedwindshield. However, a vehicle operator viewing an object such as ahead-up display at a 90° angle through the bottom portion of thewindshield will observe a double image for the reason discussed above.Thus, a windshield having a partial wedge area such as the windshieldtypes shown in FIGS. 5 and 6 would be advantageous over a windshield ofthe type shown in FIG. 3 that has a taper or wedge from the top edge ofthe windshield to the opposite or bottom edge.

In the following discussions regarding FIGS. 5 and 6, the left hand sideof windshields 330 and 430 as viewed in FIGS. 5 and 6, respectively, isthe top end of the windshield as mounted in a vehicle and the right sideas viewed in FIGS. 5 and 6 is the opposite or bottom end of thewindshield as mounted. If a shade band (shown only in FIG. 7) of a typewell known in the art were incorporated into windshields 330 and 430, itwould be positioned at the left side or top end of the windshield. Withreference to FIG. 5, the windshield 330 has glass plies 332 and 334secured to each other about interlayer 336. The windshield 330 has apartial wedge by providing outer surface 338 of the glass ply 332nonparallel to the outer surface 340 of glass ply 334 in the mid-area337 and the outer surfaces 338 and 340 of the glass plies 332 and 334,respectively, in the upper area 342 and lower area 344 parallel to oneanother. This may be accomplished by providing the glass plies 332 and334 with a constant thickness throughout their length, i.e. from the topedge to the bottom edge of the windshield, and width, i.e. from one sideto the other side (only one side shown in FIGS. 5 and 6), and aninterlayer 336 with a predetermined non-uniform thickness profile toposition the desired wedge in the windshield at the required location.More specifically, the portions of interlayer 336 in the top and bottomareas 342 and 344, respectively, of the windshield 330 are provided witha constant thickness and the portion of the interlayer in the mid-area337 are provided with a tapered thickness.

A windshield of the type shown in FIG. 5 may be constructed using asheet 336 of polyvinylbutyral that has a constant thickness in area 342of about 0.034 to 0.040 inches (0.086 to 0.102 cm), a constant thicknessin area 344 of about 0.027 to 0.030 inches (0.069 to 0.076 cm), andvarying thickness in area 337 that decreases, preferably uniformly, fromthe constant thickness in area 342 to the constant thickness in area344. As an example, windshield 330 may include a pair of 0.090 inch (2.3mm) thick glass plies 332, 334. The glass plies would each have a lengthfrom top to bottom of approximately 45 inches (114.3 cm). A sheet 336 ofpolyvinylbutyral preferably having a shape as shown in FIG. 7 would becut to fit between the glass plies. The polyvinylbutyral sheet 336 wouldhave a constant thickness of 0.034 inches (0.086 cm) from the top edgeto a distance of 25 inches (63.5 cm) therefrom (top area 342); a taperdefined by a thickness of 0.034 inches (0.086 cm) at a point spaced 25inches (63.5 cm) from the top edge of the windshield and a thickness of0.030 inches (0.076 cm) at a point 37 inches (94 cm) from the top of awindshield (mid area 337), and a constant thickness of 0.030 inches(0.076 cm) from a point 37 inches (94 cm) from the top edge to thebottom edge (bottom area 344).

FIG. 6 illustrates another embodiment of the invention directed topartial wedging of the windshield. The windshield 430 shown in FIG. 6has a pair of glass plies 432 and 434 about an interlayer 436. Thethickness of the glass plies and interlayer are selected to provide thewindshield with a lower area 437 having outer surface 438 and 440nonparallel to one another and upper area 439 having outer surfaces 438and 440 of the windshield parallel to one another. In FIG. 6, thisarrangement may be achieved by using glass plies 432 and 434 of constantthickness and a sheet of interlayer material 446 having a non-uniformthickness profile that has a constant thickness at its upper portion anda taper at its lower portion.

A windshield of the type shown in FIG. 6 may be constructed using asheet 436 of polyvinylbutyral that has a constant-thickness in area 439of about 0.034 to 0.040 inches (0.086 to 0.102 cm) and varying thicknessin area 437 that decreases, preferably uniformly, from the constantthickness in area 439 to a thickness along its lower edge of about 0.027to 0.030 inches (0.069 to 0.076 cm). As an example, the windshield 430may include a pair of 0.090 inch (2.3 mm) thick glass plies 432, 434.The glass plies would each have a length of 45 inches (114.3 cm). Asheet 436 of polyvinylbutyral preferably having a shape shown in FIG. 7,would be cut to fit between the glass plies. The sheet 436 would have aconstant thickness of 0.038 inches (0.097 cm) from the top edge to adistance of 25 inches (63.5 cm) therefrom (upper area 439) and a taperdefined by a thickness of 0.038 inches (0.097 cm) at a point spaced 25inches (63.5 cm) from the top edge to a thickness of 0.030 inches (0.076cm) at the bottom edge (lower area 437).

Referring to FIG. 1, it has been observed that windshields of theconstruction discussed above and shown in FIGS. 5 and 6 mounted in avehicle at an installation angle Y of approximately 30° with an angle ofincident Z between the mid-section 337 of the windshield 330 or thelower area 437 of the windshield 430 and the image source 14 ofapproximately 65° significantly reduces the amount of double imaging ina head-up display system as compared to the prior art windshield havinga non-wedged configuration while maintaining the optical properties ofthe prior art windshield in the upper and lower areas 342 and 344 of thewindshield 330 and the upper area 439 of the windshield 430.

In the windshield construction of the type shown in FIGS. 5 and 6, thenon-tapered sections, e.g., areas 342 and 344 of the windshield 330 ofFIG. 5 and area 449 of the windshield 430 of FIG. 6, there will beminimal, if any, optical distortion because the outer surfaces of thewindshield in those portions are parallel.

As discussed earlier, interlayers 336 and 436 may be formed by casting,extrusion, or differential stretching or a combination of theseprocesses. It should be appreciated that differential stretching of theinterlayer and subsequent cutting of the interlayer into blanks forincorporation into the windshield, results in an interlayer blank 500having a peripheral configuration that is generally quadrilateral inshape with two opposing acurate sides 502 and 504 as shown in FIG. 7. Itshould further be appreciated that the stretching also facilitates theuse of interlayer having a shade band 506, as is widely used in the art.More particularly, interlayer 500 is generally supplied as a continuousribbon or web of material having straight, longitudinally extendingopposing edges and a shade band incorporated into the web along andgenerally parallel to an upper edge of the web. The differentialstretching operation stretches the bottom edge 504 of the interlayermore than the top edge 502 so that the initially opposing straight edgesare formed into opposing arcuate edges. This stretching may beaccomplished in a continuous manner by passing the continuous web over aseries of shaping rolls. For example, the web is moved successively overa cylindrical heating roll to heat the interlayer prior to stretching, aconical heating roll to differentially stretch the interlayer to adesired contour, and a conical cooling roll to maintain the web'sstretched configuration, as disclosed in U.S. Pat. No. 4,554,713. As analternative, the interlayer web may be stretched in a batch fashion bywrapping a predetermined amount of interlayer around an adjustablecylindrical roll and expanding portions of the roll to form a conicalsurface with the circumference of the expanded roll at the endcorresponding to the bottom of the interlayer being greater than thecircumference at the opposite end, i.e. the end corresponding to the topof the interlayer, as disclosed in U.S. Pat. No. 4,201,351. During thisstretching operation, the thickness of the interlayer is reduced, withthis reduction being larger at the bottom of the interlayer since it isstretched a greater amount than the top portion.

As a result, if the sheet 336 is initially formed so that it has aconstant thickness in areas 342 and 344, and the sheet is differentiallystretched, as discussed above, to a shape a shown in FIG. 7, sheet 336in areas 342 and 344 would not have a constant thickness but rather havea slight taper as shown in FIG. 8. Although not limiting in the presentinvention, it is expected that the taper would be on the order of 0.001to 0.003 inches over a 25 inch distance (0.025 to 0.076 mn over 63.5cm). It is noted that this rate of taper, i.e. the change in thicknessover a given length, is less than the rate of taper in areas 337 and 437of interlayers 336 and 436, respectively, which correspond to thedisplay areas of the windshield. For example, interlayer 536 of the typeshown in FIG. 8 would have a thickness that decreases in upper area 542from about 0.034 to 0.040 inches (0.086 to 0.102 cm) along upper edge502 to 0.031 to 0.039 inches (0.079 to 0.099 cm), decreases in mid-area537 from about 0.031 to 0.039 inches (0.079 to 0.099 cm) to 0.028 to0.030 inches (0.071 to 0.076 cm), and decreases in lower area 544 fromabout 0.028 to 0.030 inches (0.071 to 0.076 cm) to 0.027 to 0.029 inches(0.069 to 0.074 cm) along lower edge 504. If desired, to compensate forthis tapering, the sheet 336 in FIG. 5 may be initially formed to athickness profile such that after differential stretching, areas 342 and344 each have a constant thickness. More particularly, the interlayer336 may be initially cast or extruded with areas 342 and 344 having aslightly tapered thickness profile, with their thickness increasing fromthe top edge towards the bottom edge of the interlayer as shown in FIG.9 so that after differential stretching, their profiles will have aconstant thickness. For example, interlayer 636 of the type shown inFIG. 9 would have a thickness that increases in upper area 642 fromabout 0.034 to 0.040 inches (0.086 to 0.102 cm) along upper edge 602 to0.035 to 0.043 inches (0.089 to 0.109 cm), decreases in mid-area 637from about 0.035 to 0.043 inches (0.089 to 0.109 cm) to 0.028 to 0.035inches (0.071 to 0.089 cm), and increases in lower area 644 from about0.028 to 0.035 inches (0.071 to 0.089 cm) to 0.029 to 0.036 inches(0.074 to 0.091 cm) along lower edge 604.

Similarly, if sheet 436 in FIG. 6 initially has a constant thickness inarea 439 and is differentially stretched, the interlayer in area 439will have a slight taper as shown in FIG. 10. For example, interlayer736 of the type shown in FIG. 10 would have a thickness that decreasesin upper area 739 from about 0.034 to 0.040 inches (0.086 to 0.102 cm)along upper edge 702 to 0.031 to 0.039 inches (0.079 to 0.099 cm) anddecreases in lower area 737 from about 0.031 to 0.039 inches (0.079 to0.099 cm) to 0.027 to 0.030 inches (0.069 to 0.076 cm) along lower edge704. If desired, sheet 436 of FIG. 6 may be formed to an initialthickness profile such that after differential stretching, area 439 ofsheet 436 has a constant thickness. More particularly, the interlayer436 may be initially cast or extruded with area 439 having a slightlytapered thickness profile, with its thickness increasing from the topedge towards the bottom edge of the interlayer so that afterdifferential stretching, its profiles will have a constant thickness asshown in FIG. 11. For example, interlayer 836 of the type shown in FIG.11 would have a thickness that increases in upper area 839 from about0.034 to 0.040 inches (0.086 to 0.102 cm) along upper edge 802 to 0.035to 0.043 inches (0.089 to 0.109 cm) and decreases in lower area 837 fromabout 0.035 to 0.043 inches (0.089 to 0.109 cm) to 0.029 to 0.036 inches(0.074 to 0.091 cm) along lower edge 804.

It should be further appreciated that even with windshieldconfigurations where interlayer areas 542 and 544 shown in FIG. 8 andarea 739 shown in FIG. 10 have a slight taper, any optical distortion inthese areas due to the outer surfaces of. the windshield beingnon-parallel would be minimal.

Refereeing to FIG. 7, the stretching operation also forms the shade band506 along arcuate path so that when the interlayer 500 is positionedbetween two glass plies and the assembly is laminated to form awindshield, the shade band 506 remains generally parallel with the upperedge of the windshield. In this manner, when the windshield is installedin a vehicle, the shade band 506 will have a generally horizontalorientation.

Cast or extruded interlayer may also be made to provide the same blankperipheral contour as shown in FIG. 7, with or without the contouredshade band.

It is obvious that multiple sheets of polyvinylbutyral interlayer may beused in place of the single sheets 336, 436, 536, 636, 736 and 836provided that when they are used in combination, the resultingmulti-layered interlayer has the same thickness profiles as discussedabove with respect to a single interlayer blank.

As can now be appreciated, the partial wedging of the windshields 330and 430 can be attained in any convenient manner. For example, one ormore of the glass plies may have varying thicknesses and/or theinterlayer may have varying thicknesses in the wedged sections, i.e.area 337 of the windshield 330 and area 437 for the windshield 430. Therequirement in the practice of the invention is that when the windshieldis assembled using the glass plies and interlayer, selected areas of thewindshield have the outer surfaces nonparallel to one another while theother areas have the outer surfaces parallel or nearly parallel. As usedherein and as can now be appreciated the term “outer surface parallel”does not require the surfaces to be perfectly parallel to one anotherbut have the degree of parallelism that is usually observed in the priorart windshields to which this invention is directed. The invention alsoincludes windshield configurations where the outer major surfaces of thewindshield in the non-display areas are not parallel but are angularlyoffset a small amount which is less than the offset in the display area,as discussed above. Further, the invention was discussed with thewindshield having the tapered area extending from side to side; however,as can now be appreciated only the area in front of the observer mayhave the partial wedge with the remaining area of the windshield havingparallel outer surfaces.

Further from the foregoing discussion, it can now be appreciated thatthe invention may be practiced by tapering selected sections of a sheetof interlayer, by providing a piece of tapered interlayer over a sheetof interlayer having a constant thickness, by providing a glass plyhaving selected portions tapered by adding a piece of tapered glass to aglass ply having a constant thickness and/or by removing glass, e.g., bygrinding and polishing a selected section of the glass.

Still further, the invention may be practiced using colored glass of thetype known in the art, e.g. such as that taught in U.S. Pat. No.4,792,536, may be used on windshields having environmental coatings,e.g., of the type taught in U.S. Pat. No. 4,610,771, may be used onheatable windshields, e.g., of the type taught in U.S. Pat. No.4,820,902 or may be used with a coating on any surface of the glassplies at least in the area of the windshield having nonparallel outersurfaces to enhance the image, e.g., coatings of the type taught in U.S.Pat. No. 3,899,241, which teachings of these patents are herebyincorporated by reference.

The forms of this invention shown and described in this disclosurerepresent illustrative preferred embodiments and various modificationsthereof. It is understood that various changes may be made withoutdeparting from the scope of the invention as defined by the claimedsubject matter which follows.

I claim:
 1. An automotive transparency for use with a heads-up displaysystem comprising: a first glass ply; a second glass ply, the first andsecond glass plies each having a constant thickness of 0.090 inch and adistance between top of the plies to bottom of the plies of 45 inches;an interlayer between the first and second glass plies; the interlayerhas a top edge and an opposite bottom edge, the interlayer having aconstant thickness of 0.038 inch from the top edge to a distance of 25inches therefrom defined as a thickness change line and a taper from thethickness change line to the bottom edge of the interlayer, wherein thethickness of the interlayer at the thickness change line is 0.038 inchand at the bottom edge is 0.030 inch.
 2. An automotive transparencycomprising: a first glass ply and a second glass ply each having aconstant thickness of 0.090 inch and a length of 45 inches; and aninterlayer between the first glass ply and second glass ply and having aconstant thickness in a first predetermined area and a varying thicknessin a second predetermined area, wherein the first predetermined area ofthe interlayer is adjacent a top edge of the interlayer and the secondpredetermined area of the interlayer is adjacent a bottom edge of theinterlayer, and the first predetermined area of the interlayer has aconstant thickness of 0.038 inch from the top edge to a distance of 25inches therefrom defined at a thickness change line and the secondpredetermined area of the interlayer has a taper from the thicknesschange line to the bottom edge of the interlayer, and the thickness ofthe interlayer at the thickness change line is 0.038 inch and at thebottom edge is 0.030 inch.
 3. The automotive transparency of claim 2wherein the interlayer is a sheet of polyvinylbutyral.
 4. The automotivetransparency of claim 2 used in combination with a heads-up displaysystem comprises: means to project a desired display having first andsecond light rays, and means for mounting the automotive transparencyand said means to project relative-to one another to direct the firstand second light rays toward the second predetermined area.
 5. Theautomotive transparency of claim 2 wherein the interlayer is a plasticinterlayer.
 6. A vehicle windshield for a head-up display comprising: afirst glass ply having a constant thickness; a second glass ply having aconstant thickness; and a polyvinylbutyral interlayer having a constantthickness in a first predetermined area and a varying thickness in asecond predetermined area; the first glass ply and second glass plysecured together by the interlayer material to form a laminate having afirst outer major surface, an opposing second outer major surface, afirst predetermined area defined by the first predetermined area of theinterlayer over which the outer major surfaces are substantiallyparallel to one another, and a second predetermined area defined by thesecond predetermined area of the interlayer over which the outer majorsurfaces are nonparallel to one another, wherein the windshield has alength of 45 inches, the first predetermined area of the interlayer isadjacent the top of the windshield and extends for a distance of 25inches and the second predetermined area of the windshield has awedge-shaped thickness profile.
 7. An interlayer blank for securingglass plies together comprising: a first predetermined area having aconstant thickness of 0.038 inch and a second predetermined area havinga varying thickness, the interlayer having a top edge and a bottom edge,wherein the first predetermined area of the interlayer is adjacent thetop edge and the second predetermined area of the interlayer is adjacentthe bottom edge and the first predetermined area of the interlayer has aconstant thickness from the top edge to a distance of 25 inchestherefrom defined as a thickness change line and the secondpredetermined area has a taper from the thickness change line to thebottom edge of the interlayer, wherein the thickness of the interlayerat the thickness change line is 0.038 inch and that the bottom edge is0.030 inch.
 8. The interlayer blank of claim 7 wherein the interlayerblank is a sheet of polyvinylbutyral and the second predetermined areaviewed in cross-section has a wedged shape.
 9. The interlayer blank ofclaim 7 wherein the interlayer blank is a sheet of polyvinylbutyral. 10.The interlayer blank of claim 7 wherein the interlayer is a sheet ofpolyvinylbutyral, and the distance between top of the interlayer blankand bottom of the interlayer blank is 45 inches.
 11. The interlayerblank of claim 2 wherein the top edge has a shade band.